The increasing electricity demand and cost, in addition to the increasing global energy demands, are the main motivations in seeking for sustainable new technologies in the ﬁeld of energy conversion and utilization. Various thermodynamic cycles, such as organic Rankine cycle (ORC), supercritical Rankine cycle, supercritical Brayton cycle, Kalina cycle and trilateral ﬂash cycle, have been proposed to convert the low-grade heat sources into electricity. ORC is extremely popular for generating electricity from a wide variety of heat sources, such as industrial waste heat, solar energy, geothermal energy, waste heat from internal combustion engine, etc. For large systems (> 5 MW), typically axial turbine expanders are the preferred design. However successful implementation of any of these cycles requires availability of systems less than 5 MW scale and definitely at less than 1 MW. The critical component in these small scale system is a positive displacement expander. Examples of positive displacement expanders are linear piston expanders, rotary wankel engine type expanders, etc. The development of a cost effective positive displacement expander that is not only efficient but also inexpensive is critical for the success of small scale electricity generation systems.
Power production from combustion of fossil fuels, such as coal and natural gas, releases carbon dioxide (CO2) and contributes to rising greenhouse gas (GHG) levels in the atmosphere. Technologies capable of cost-effective CO2 capture and reuse would help stabilize atmospheric GHG levels and provide an opportunity to turn CO2 into a feedstock for valuable products, such as chemicals and fuels. From producing carbon monoxide (synthetic gas), to plastics, to algae, etc are some of the potential applications of converting high pressure CO2 into valuable higher value chemicals. Successful development of technology could potentially create an entirely new industry where waste CO2–rather than oil–is used to produce gasoline, diesel fuel, jet fuel, and industrial chemicals. Other benefits include reduce petroleum imports, reduce economic impact on the country due to spikes in petroleum prices, and stabilize atmospheric GHG levels.
Development of a High Pressure Linear expander/generator for sCO2 Brayton Cycle.
The increasing electricity demand and cost, in addition to the increasing global energy demands, are the main motivations in seeking for sustainable new technologies in the ﬁeld of energy conversion and utilization. Various thermodynamic cycles, such as organic Rankine cycle (ORC), supercritical Rankine cycle, supercritical Brayton cycle, have been proposed to convert heat sources into electricity. There has been a significant research in sCO2 Brayton throughout the world including India. The application for sCO2 Brayton cycle to generate electricity from a wide variety of heat sources include natural gas, solar energy, geothermal energy, and waste heat from a variety of industrial processes and internal combustion engine. For large systems (> 10 MW), typically axial turbine expanders are the preferred design. However there is a significant need for systems less than 1 MW. Given the high power density of sCO2, rotary expanders are not practical due to its high speed resulting in low efficiencies and high capital costs. A linear expander can address this need. The development of a cost effective positive displacement expander that is not only efficient but also inexpensive is critical for the success of small scale sCO2 electricity generation systems
An isothermal process is a change of a system, in which the temperature remains constant: ΔT = 0. This typically occurs when a system is in contact with an outside thermal reservoir (heat bath), and the change will occur slowly enough to allow the system to continually adjust to the temperature of the reservoir through heat exchange. In contrast, an adiabatic process is where a system exchanges no heat with its surroundings (Q = 0). In other words, in an isothermal process, the value ΔT = 0 and therefore ΔU = 0 (only for an ideal gas) but Q ≠ 0, while in an adiabatic process, ΔT ≠ 0 but Q = 0. In reality, an isothermal compressor is an old dream of the engineer, but successful implementation could improve the efficiency of various industrial and power generation plants significantly, and it can save power in many compression jobs in process plants, especially in cases of high pressure ratio.
The ideal isothermal compressor has not yet been built, with one historic exception. But approximations with adiabatic compressor stages alternating with intercoolers are widely used. The intermediate pressure level for the intercooling steps has to be chosen such that the adiabatic discharge temperatures in each compression step are all equal for the given pressure ratio. Typically, one intercooling step provides more than half the power saving ideally attainable. It is also useful to look at power saving as a function of the number of intercooling steps.
A novel design is needed to reduce the power consumption of compressors throughout the industry and result in significant benefits to the society.
With the increase use of energy, efficient small and distributable energy generation systems are needed to meet these demands. The oxy-combustion process is a proven technology for obtaining high combustion temperatures and results in an increased power generation efficiency from a given fossil fuel source and decreased greenhouse gas (GHG) emission. About 65% of an oxy-combustion plant net efficiency loss is due to electric power requirements by an air separation unit (ASU) . Currently the generation of O2 is economically viable only for larger electricity generation systems which need about 3,000 tons/day of O2. For the smaller generation process, where the requirements are of the order of 10 tons/day of O2, a cost effective method to generate O2 does not exist.
Currently O2 is separated from air using the traditional cryogenic separation process, cryogenic distillation-based air separation is costly and energy-intensive to operate. This process is energy intensive and consumes over 200 kWh of electricity per ton of O2 produced for plants in the range of 3,000 tpd of O2 produced. According to a large manufacturer of industrial gases, almost as much as 1,000 kWh is needed for a 10 tpd plant. In summary, the energy consumption of current cryogenic technologies is four to five times the theoretical minimum energy required for the process. The elimination of the energy consumption gap between theoretical and practical for small plants would decrease the O2 production costs and enable oxy-combustion as a viable option in small power generation systems.